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tailscale/wgengine/magicsock/legacy.go

642 lines
18 KiB
Go

// Copyright (c) 2019 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package magicsock
import (
"bytes"
"crypto/hmac"
"crypto/subtle"
"encoding/binary"
"errors"
"hash"
"net"
"strings"
"sync"
"time"
"golang.org/x/crypto/blake2s"
"golang.org/x/crypto/chacha20poly1305"
"golang.org/x/crypto/poly1305"
"golang.zx2c4.com/wireguard/conn"
"golang.zx2c4.com/wireguard/tai64n"
"inet.af/netaddr"
"tailscale.com/ipn/ipnstate"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/types/wgkey"
"tailscale.com/wgengine/wgcfg"
)
var (
errNoDestinations = errors.New("magicsock: no destinations")
errDisabled = errors.New("magicsock: legacy networking disabled")
)
// createLegacyEndpointLocked creates a new wireguard-go endpoint for a legacy connection.
// pk is the public key of the remote peer. addrs is the ordered set of addresses for the remote peer.
// rawDest is the encoded wireguard-go endpoint string. It should be treated as a black box.
// It is provided so that addrSet.DstToString can return it when requested by wireguard-go.
func (c *Conn) createLegacyEndpointLocked(pk key.Public, addrs wgcfg.IPPortSet, rawDest string) (conn.Endpoint, error) {
if c.disableLegacy {
return nil, errDisabled
}
a := &addrSet{
Logf: c.logf,
publicKey: pk,
curAddr: -1,
rawdst: rawDest,
}
a.ipPorts = append(a.ipPorts, addrs.IPPorts()...)
// If this endpoint is being updated, remember its old set of
// endpoints so we can remove any (from c.addrsByUDP) that are
// not in the new set.
var oldIPP []netaddr.IPPort
if preva, ok := c.addrsByKey[pk]; ok {
oldIPP = preva.ipPorts
}
c.addrsByKey[pk] = a
// Add entries to c.addrsByUDP.
for _, ipp := range a.ipPorts {
if ipp.IP() == derpMagicIPAddr {
continue
}
c.addrsByUDP[ipp] = a
}
// Remove previous c.addrsByUDP entries that are no longer in the new set.
for _, ipp := range oldIPP {
if ipp.IP() != derpMagicIPAddr && c.addrsByUDP[ipp] != a {
delete(c.addrsByUDP, ipp)
}
}
return a, nil
}
func (c *Conn) findLegacyEndpointLocked(ipp netaddr.IPPort, packet []byte) conn.Endpoint {
if c.disableLegacy {
return nil
}
// Pre-disco: look up their addrSet.
if as, ok := c.addrsByUDP[ipp]; ok {
as.updateDst(ipp)
return as
}
// We don't know who this peer is. It's possible that it's one of
// our legitimate peers and they've roamed to an address we don't
// know. If this is a handshake packet, we can try to identify the
// peer in question.
if as := c.peerFromPacketLocked(packet); as != nil {
as.updateDst(ipp)
return as
}
// We have no idea who this is, drop the packet.
//
// In the past, when this magicsock implementation was the main
// one, we tried harder to find a match here: we would pass the
// packet into wireguard-go with a "singleEndpoint" implementation
// that wrapped the UDPAddr. Then, a patch we added to
// wireguard-go would call UpdateDst on that singleEndpoint after
// decrypting the packet and identifying the peer (if any),
// allowing us to update the relevant addrSet.
//
// This was a significant out of tree patch to wireguard-go, so we
// got rid of it, and instead switched to this logic you're
// reading now, which makes a best effort to identify sources for
// handshake packets (because they're relatively easy to turn into
// a peer public key statelessly), but otherwise drops packets
// that come from "roaming" addresses that aren't known to
// magicsock.
//
// The practical consequence of this is that some complex NAT
// traversal cases will now fail between a very old Tailscale
// client (0.96 and earlier) and a very new Tailscale
// client. However, those scenarios were likely also failing on
// all-old clients, because the probabilistic NAT opening didn't
// work reliably. So, in practice, this simplification means
// connectivity looks like this:
//
// - old+old client: unchanged
// - old+new client (easy network topology): unchanged
// - old+new client (hard network topology): was bad, now a bit worse
// - new+new client: unchanged
//
// This degradation is acceptable in that it continues to support
// the incremental upgrade of old clients that currently work
// well, which is our primary goal for the <100 clients still left
// on the oldest pre-DERP versions (as of 2021-01-12).
return nil
}
func (c *Conn) resetAddrSetStatesLocked() {
for _, as := range c.addrsByKey {
as.curAddr = -1
as.stopSpray = as.timeNow().Add(sprayPeriod)
}
}
func (c *Conn) sendAddrSet(b []byte, as *addrSet) error {
if c.disableLegacy {
return errDisabled
}
var addrBuf [8]netaddr.IPPort
dsts, roamAddr := as.appendDests(addrBuf[:0], b)
if len(dsts) == 0 {
return errNoDestinations
}
var success bool
var ret error
for _, addr := range dsts {
sent, err := c.sendAddr(addr, as.publicKey, b)
if sent {
success = true
} else if ret == nil {
ret = err
}
if err != nil && addr != roamAddr && c.sendLogLimit.Allow() {
if c.connCtx.Err() == nil { // don't log if we're closed
c.logf("magicsock: Conn.Send(%v): %v", addr, err)
}
}
}
if success {
return nil
}
return ret
}
// peerFromPacketLocked extracts returns the addrSet for the peer who sent
// packet, if derivable.
//
// The derived addrSet is a hint, not a cryptographically strong
// assertion. The returned value MUST NOT be used for any security
// critical function. Callers MUST assume that the addrset can be
// picked by a remote attacker.
func (c *Conn) peerFromPacketLocked(packet []byte) *addrSet {
if len(packet) < 4 {
return nil
}
msgType := binary.LittleEndian.Uint32(packet[:4])
if msgType != messageInitiationType {
// Can't get peer out of a non-handshake packet.
return nil
}
var msg messageInitiation
reader := bytes.NewReader(packet)
err := binary.Read(reader, binary.LittleEndian, &msg)
if err != nil {
return nil
}
// Process just enough of the handshake to extract the long-term
// peer public key. We don't verify the handshake all the way, so
// this may be a spoofed packet. The extracted peer MUST NOT be
// used for any security critical function. In our case, we use it
// as a hint for roaming addresses.
var (
pub = c.privateKey.Public()
hash [blake2s.Size]byte
chainKey [blake2s.Size]byte
peerPK key.Public
boxKey [chacha20poly1305.KeySize]byte
)
mixHash(&hash, &initialHash, pub[:])
mixHash(&hash, &hash, msg.Ephemeral[:])
mixKey(&chainKey, &initialChainKey, msg.Ephemeral[:])
ss := c.privateKey.SharedSecret(key.Public(msg.Ephemeral))
if isZero(ss[:]) {
return nil
}
kdf2(&chainKey, &boxKey, chainKey[:], ss[:])
aead, _ := chacha20poly1305.New(boxKey[:])
_, err = aead.Open(peerPK[:0], zeroNonce[:], msg.Static[:], hash[:])
if err != nil {
return nil
}
return c.addrsByKey[peerPK]
}
func shouldSprayPacket(b []byte) bool {
if len(b) < 4 {
return false
}
msgType := binary.LittleEndian.Uint32(b[:4])
switch msgType {
case messageInitiationType,
messageResponseType,
messageCookieReplyType: // TODO: necessary?
return true
}
return false
}
const sprayPeriod = 3 * time.Second
// appendDests appends to dsts the destinations that b should be
// written to in order to reach as. Some of the returned IPPorts may
// be fake addrs representing DERP servers.
//
// It also returns as's current roamAddr, if any.
func (as *addrSet) appendDests(dsts []netaddr.IPPort, b []byte) (_ []netaddr.IPPort, roamAddr netaddr.IPPort) {
spray := shouldSprayPacket(b) // true for handshakes
now := as.timeNow()
as.mu.Lock()
defer as.mu.Unlock()
as.lastSend = now
// Spray logic.
//
// After exchanging a handshake with a peer, we send some outbound
// packets to every endpoint of that peer. These packets are spaced out
// over several seconds to make sure that our peer has an opportunity to
// send its own spray packet to us before we are done spraying.
//
// Multiple packets are necessary because we have to both establish the
// NAT mappings between two peers *and use* the mappings to switch away
// from DERP to a higher-priority UDP endpoint.
const sprayFreq = 250 * time.Millisecond
if spray {
as.lastSpray = now
as.stopSpray = now.Add(sprayPeriod)
// Reset our favorite route on new handshakes so we
// can downgrade to a worse path if our better path
// goes away. (https://github.com/tailscale/tailscale/issues/92)
as.curAddr = -1
} else if now.Before(as.stopSpray) {
// We are in the spray window. If it has been sprayFreq since we
// last sprayed a packet, spray this packet.
if now.Sub(as.lastSpray) >= sprayFreq {
spray = true
as.lastSpray = now
}
}
// Pick our destination address(es).
switch {
case spray:
// This packet is being sprayed to all addresses.
for i := range as.ipPorts {
dsts = append(dsts, as.ipPorts[i])
}
if as.roamAddr != nil {
dsts = append(dsts, *as.roamAddr)
}
case as.roamAddr != nil:
// We have a roaming address, prefer it over other addrs.
// TODO(danderson): this is not correct, there's no reason
// roamAddr should be special like this.
dsts = append(dsts, *as.roamAddr)
case as.curAddr != -1:
if as.curAddr >= len(as.ipPorts) {
as.Logf("[unexpected] magicsock bug: as.curAddr >= len(as.ipPorts): %d >= %d", as.curAddr, len(as.ipPorts))
break
}
// No roaming addr, but we've seen packets from a known peer
// addr, so keep using that one.
dsts = append(dsts, as.ipPorts[as.curAddr])
default:
// We know nothing about how to reach this peer, and we're not
// spraying. Use the first address in the array, which will
// usually be a DERP address that guarantees connectivity.
if len(as.ipPorts) > 0 {
dsts = append(dsts, as.ipPorts[0])
}
}
if logPacketDests {
as.Logf("spray=%v; roam=%v; dests=%v", spray, as.roamAddr, dsts)
}
if as.roamAddr != nil {
roamAddr = *as.roamAddr
}
return dsts, roamAddr
}
// addrSet is a set of UDP addresses that implements wireguard/conn.Endpoint.
//
// This is the legacy endpoint for peers that don't support discovery;
// it predates discoEndpoint.
type addrSet struct {
publicKey key.Public // peer public key used for DERP communication
// ipPorts is an ordered priority list provided by wgengine,
// sorted from expensive+slow+reliable at the begnining to
// fast+cheap at the end. More concretely, it's typically:
//
// [DERP fakeip:node, Global IP:port, LAN ip:port]
//
// But there could be multiple or none of each.
ipPorts []netaddr.IPPort
// clock, if non-nil, is used in tests instead of time.Now.
clock func() time.Time
Logf logger.Logf // must not be nil
mu sync.Mutex // guards following fields
lastSend time.Time
// roamAddr is non-nil if/when we receive a correctly signed
// WireGuard packet from an unexpected address. If so, we
// remember it and send responses there in the future, but
// this should hopefully never be used (or at least used
// rarely) in the case that all the components of Tailscale
// are correctly learning/sharing the network map details.
roamAddr *netaddr.IPPort
// curAddr is an index into addrs of the highest-priority
// address a valid packet has been received from so far.
// If no valid packet from addrs has been received, curAddr is -1.
curAddr int
// stopSpray is the time after which we stop spraying packets.
stopSpray time.Time
// lastSpray is the last time we sprayed a packet.
lastSpray time.Time
// loggedLogPriMask is a bit field of that tracks whether
// we've already logged about receiving a packet from a low
// priority ("low-pri") address when we already have curAddr
// set to a better one. This is only to suppress some
// redundant logs.
loggedLogPriMask uint32
// rawdst is the destination string from/for wireguard-go.
rawdst string
}
// derpID returns this addrSet's home DERP node, or 0 if none is found.
func (as *addrSet) derpID() int {
for _, ua := range as.ipPorts {
if ua.IP() == derpMagicIPAddr {
return int(ua.Port())
}
}
return 0
}
func (as *addrSet) timeNow() time.Time {
if as.clock != nil {
return as.clock()
}
return time.Now()
}
var noAddr, _ = netaddr.FromStdAddr(net.ParseIP("127.127.127.127"), 127, "")
func (a *addrSet) dst() netaddr.IPPort {
a.mu.Lock()
defer a.mu.Unlock()
if a.roamAddr != nil {
return *a.roamAddr
}
if len(a.ipPorts) == 0 {
return noAddr
}
i := a.curAddr
if i == -1 {
i = 0
}
return a.ipPorts[i]
}
func (a *addrSet) DstToBytes() []byte {
return packIPPort(a.dst())
}
func (a *addrSet) DstToString() string {
return a.rawdst
}
func (a *addrSet) DstIP() net.IP {
return a.dst().IP().IPAddr().IP // TODO: add netaddr accessor to cut an alloc here?
}
func (a *addrSet) SrcIP() net.IP { return nil }
func (a *addrSet) SrcToString() string { return "" }
func (a *addrSet) ClearSrc() {}
// updateDst records receipt of a packet from new. This is used to
// potentially update the transmit address used for this addrSet.
func (a *addrSet) updateDst(new netaddr.IPPort) error {
if new.IP() == derpMagicIPAddr {
// Never consider DERP addresses as a viable candidate for
// either curAddr or roamAddr. It's only ever a last resort
// choice, never a preferred choice.
// This is a hot path for established connections.
return nil
}
a.mu.Lock()
defer a.mu.Unlock()
if a.roamAddr != nil && new == *a.roamAddr {
// Packet from the current roaming address, no logging.
// This is a hot path for established connections.
return nil
}
if a.roamAddr == nil && a.curAddr >= 0 && new == a.ipPorts[a.curAddr] {
// Packet from current-priority address, no logging.
// This is a hot path for established connections.
return nil
}
index := -1
for i := range a.ipPorts {
if new == a.ipPorts[i] {
index = i
break
}
}
publicKey := wgkey.Key(a.publicKey)
pk := publicKey.ShortString()
old := "<none>"
if a.curAddr >= 0 {
old = a.ipPorts[a.curAddr].String()
}
switch {
case index == -1:
if a.roamAddr == nil {
a.Logf("[v1] magicsock: rx %s from roaming address %s, set as new priority", pk, new)
} else {
a.Logf("[v1] magicsock: rx %s from roaming address %s, replaces roaming address %s", pk, new, a.roamAddr)
}
a.roamAddr = &new
case a.roamAddr != nil:
a.Logf("[v1] magicsock: rx %s from known %s (%d), replaces roaming address %s", pk, new, index, a.roamAddr)
a.roamAddr = nil
a.curAddr = index
a.loggedLogPriMask = 0
case a.curAddr == -1:
a.Logf("[v1] magicsock: rx %s from %s (%d/%d), set as new priority", pk, new, index, len(a.ipPorts))
a.curAddr = index
a.loggedLogPriMask = 0
case index < a.curAddr:
if 1 <= index && index <= 32 && (a.loggedLogPriMask&1<<(index-1)) == 0 {
a.Logf("[v1] magicsock: rx %s from low-pri %s (%d), keeping current %s (%d)", pk, new, index, old, a.curAddr)
a.loggedLogPriMask |= 1 << (index - 1)
}
default: // index > a.curAddr
a.Logf("[v1] magicsock: rx %s from %s (%d/%d), replaces old priority %s", pk, new, index, len(a.ipPorts), old)
a.curAddr = index
a.loggedLogPriMask = 0
}
return nil
}
func (a *addrSet) String() string {
a.mu.Lock()
defer a.mu.Unlock()
buf := new(strings.Builder)
buf.WriteByte('[')
if a.roamAddr != nil {
buf.WriteString("roam:")
sbPrintAddr(buf, *a.roamAddr)
}
for i, addr := range a.ipPorts {
if i > 0 || a.roamAddr != nil {
buf.WriteString(", ")
}
sbPrintAddr(buf, addr)
if a.curAddr == i {
buf.WriteByte('*')
}
}
buf.WriteByte(']')
return buf.String()
}
func (as *addrSet) populatePeerStatus(ps *ipnstate.PeerStatus) {
as.mu.Lock()
defer as.mu.Unlock()
ps.LastWrite = as.lastSend
for i, ua := range as.ipPorts {
if ua.IP() == derpMagicIPAddr {
continue
}
uaStr := ua.String()
ps.Addrs = append(ps.Addrs, uaStr)
if as.curAddr == i {
ps.CurAddr = uaStr
}
}
if as.roamAddr != nil {
ps.CurAddr = ippDebugString(*as.roamAddr)
}
}
// Message types copied from wireguard-go/device/noise-protocol.go
const (
messageInitiationType = 1
messageResponseType = 2
messageCookieReplyType = 3
)
// Cryptographic constants copied from wireguard-go/device/noise-protocol.go
var (
noiseConstruction = "Noise_IKpsk2_25519_ChaChaPoly_BLAKE2s"
wgIdentifier = "WireGuard v1 zx2c4 Jason@zx2c4.com"
initialChainKey [blake2s.Size]byte
initialHash [blake2s.Size]byte
zeroNonce [chacha20poly1305.NonceSize]byte
)
func init() {
initialChainKey = blake2s.Sum256([]byte(noiseConstruction))
mixHash(&initialHash, &initialChainKey, []byte(wgIdentifier))
}
// messageInitiation is the same as wireguard-go's MessageInitiation,
// from wireguard-go/device/noise-protocol.go.
type messageInitiation struct {
Type uint32
Sender uint32
Ephemeral wgkey.Key
Static [wgkey.Size + poly1305.TagSize]byte
Timestamp [tai64n.TimestampSize + poly1305.TagSize]byte
MAC1 [blake2s.Size128]byte
MAC2 [blake2s.Size128]byte
}
func mixKey(dst *[blake2s.Size]byte, c *[blake2s.Size]byte, data []byte) {
kdf1(dst, c[:], data)
}
func mixHash(dst *[blake2s.Size]byte, h *[blake2s.Size]byte, data []byte) {
hash, _ := blake2s.New256(nil)
hash.Write(h[:])
hash.Write(data)
hash.Sum(dst[:0])
hash.Reset()
}
func hmac1(sum *[blake2s.Size]byte, key, in0 []byte) {
mac := hmac.New(func() hash.Hash {
h, _ := blake2s.New256(nil)
return h
}, key)
mac.Write(in0)
mac.Sum(sum[:0])
}
func hmac2(sum *[blake2s.Size]byte, key, in0, in1 []byte) {
mac := hmac.New(func() hash.Hash {
h, _ := blake2s.New256(nil)
return h
}, key)
mac.Write(in0)
mac.Write(in1)
mac.Sum(sum[:0])
}
func kdf1(t0 *[blake2s.Size]byte, key, input []byte) {
hmac1(t0, key, input)
hmac1(t0, t0[:], []byte{0x1})
}
func kdf2(t0, t1 *[blake2s.Size]byte, key, input []byte) {
var prk [blake2s.Size]byte
hmac1(&prk, key, input)
hmac1(t0, prk[:], []byte{0x1})
hmac2(t1, prk[:], t0[:], []byte{0x2})
for i := range prk[:] {
prk[i] = 0
}
}
func isZero(val []byte) bool {
acc := 1
for _, b := range val {
acc &= subtle.ConstantTimeByteEq(b, 0)
}
return acc == 1
}